1. Field of the Invention
This invention relates to a cell top for an electrolytic cell for production of alkali metal halates. More particularly, the invention comprises a chlorate cell top with a highly corrosion-resistant lightweight metallic liner and appropriate structural reinforcing means.
Alkali metal halates, e.g., sodium chlorate, can be prepared by electrolysis of an alkali metal halide, usually purified to free it of heavy metals and of magnesium and calcium compounds. The halates may be formed by the batch method or the electrolyte may be circulated continuously. Chlorate cells generally are iron tanks which are often completely lined with concrete. Cell anodes may be constructed of graphite, or of valve metals, e.g., titanium, coated on their active electrolytic surfaces with a noble metal or a noble metal oxide or equivalent, e.g., platinum, 30 to 70 weight percent iridium and platinum alloy, or other active surface materials. Cathodes are typically constructed of iron or steel. In some designs the cell body is large, and the volume of electrodes is a small fraction of the volume of electrolyte. In other designs, typically, the entire cell is taken up by the electrodes, with a relatively small electrolyte space between electrodes.
The formation of sodium chlorate by electrolysis of a brine solution represents a complex series of electrochemical and chemical reactions. The maintenance of a high operating efficiency depends upon a number of factors including temperature, pH, addition agents, and other factors. Usual current densities for production of sodium chlorate range from about 0.5 to 1.5 amperes per square inch, at an operating temperature of 85.degree. to 90.degree. C. The cell liquor product of electrolysis is typically evaporated in two stages for concentration, after which separation of sodium chlorate takes place in a crystallizer. Final separation can be obtained in a batch centrifuge, and drying can be carried out in a heated air rotary dryer, after which the material can undergo grinding, screening, and packing operations. A typical electrochemical apparatus for the manufacture of halates is described in U.S. Pat. No. 3,732,153, issued May 8, 1973 to Harke et al.
In this description of illustrative embodiments of a chlorate cell top, reference will be made to the production of sodium chlorate from an aqueous solution of sodium chloride, although it is clear that this is for the purpose of simplicity of description, since it is possible to make other alkali metal halates, e.g., sodium bromate or potassium iodate, by the methods and apparatus herein described. It is furthermore to be kept in mind that various equivalent structures may be substituted for those mentioned and replacements may be made which are apparent to one skilled in the art to which this invention pertains.